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08 November 2013

The Effects of Fructose

I recently received a little present from Hungary: a chocolate bar. I was very surprised to read on the packaging: “Suitable for diabetics”. I checked the ingredients behind, it listed 35% fructose!

The mistaken belief that fructose consumption is safe for diabetic patients comes from the research regarding Glycemic Index (GI) of different types of food. The GI measures the speed at which carbohydrates are absorbed and converted into blood sugar. The higher the GI, the greater the resulting blood sugar, the unhealthier the food.

However, defining carbohydrate foods as unhealthy just by looking at the Glycemic Index can be misleading.

For example, bread, pasta and rice (glucose) have a higher GI than table sugar (half glucose and half fructose). And the reason is the presence of fructose. Fructose alone has a very low GI. Glucose (starchy food) moves directly from small intestine into the bloodstream, only a small part of glucose is metabolized by the liver. However, almost all fructose is metabolized in the liver, it has no direct effect on blood sugar levels.

Because fructose barely elevates blood sugar, we perceive it as the ideal food for diabetics. Simple table sugar also seems less harmful that starchy food, like pasta and potato. However, research does not seem to confirm the beneficial effects of fructose.

Fructose is metabolized almost exclusively by the liver, which responds in producing more triglycerides shipped out to the bloodstream. High triglyceride levels are associated with a higher risk of heart disease.

Fructose – on the long term – causes a glucose build-up in the liver, by preventing the glucose to be metabolized. In response, our pancreas will secrete even more insulin to overcome this high glucose load in the liver. This results in the muscles to become insulin resistant, which is the first step toward diabetes and the associated condition of heart disease.

Triglycerides are the form in which energy is stored in the fat tissues. Fructose stimulates the liver to produce more triglycerides, on top of this, insulin is secreted in response to a glucose build-up in the liver, it means that fructose is very much lipogenic (fattening), it helps the accumulations of fat in the fat tissues, because of the presence of insulin (insulin prevents the break-down of triglycerides to be used as fuel, so these triglycerides remain in the fat tissues). Weight-gain is associated with a number of chronic diseases.

Another harmful effect of fructose is on AGEs. Fructose is much more reactive than glucose in forming AGEs (the cross linking of proteins and sugars in our body), leading to premature aging. Diabetics in general have more wrinkles than healthy people, it is known as diabetes induced aging. According to this study:

"In case of comparing fructose with glucose in the effects on glycation [formation of AGEs], fructose more markedly enhanced the fluorescence of glycated collagen, and reduced the digestibility of collagen by collagenase from 86.0 % to 15.9 % which suggested closer involvement of fructose rather than glucose in cross-linking.

For more information, I highly recommend to read the Wikipedia page about fructose, where you will be able to find links to the studies confirming the effects of fructose.

In conclusion, a diet high in fructose can lead to various conditions, and the labels on foods bought in stores might be based on mistaken assumptions. Just eat real food, be careful with fruits as well, they have high fructose content. Fruits are nature’s dessert: in moderation!